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Changing Landscape of Multimedia Applications

Changing Landscape of Multimedia Applications. Today: Downlink Video Broadcast. Tomorrow: Uplink Video Transmission. DFD (Displaced Frame Difference). Motion search range. +. Motion Vector. Previous frame. Current frame. Contemporary Video Coding Standards.

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Changing Landscape of Multimedia Applications

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  1. Changing Landscape of Multimedia Applications Today: Downlink Video Broadcast Tomorrow: Uplink Video Transmission

  2. DFD (Displaced Frame Difference) Motion search range + Motion Vector Previous frame Current frame Contemporary Video Coding Standards • Motion-Compensated Predictive Coding (MPEG/H.26) • High compression efficiency • Rigid complexity partition between encoder (heavy) & decoder (light) • High fragility to transmission losses • Image Coding (Motion JPEG) • Low complexity • High robustness to transmission losses • Low compression efficiency

  3. Heavy PRISM Uplink Decoder Heavy PRISM Downlink Encoder Trans-coding Proxy Light PRISM Uplink Encoder Light PRISM Downlink Decoder Rethinking Video Over Wireless Challenges: • Low bandwidths  high compression efficiency • Limited handheld battery power low end-device complexity • Lossy wireless medium robustness to transmission losses New Architecture: PRISM (Power-efficient, Robust, hIgh-compression Syndrome-based Multimedia coding) High compression efficiency Flexible partition of complexity between encoder & decoder Inbuilt robustness to channel loss Backward compatibility with existing video standards Puri & Ramchandran, Allerton ’02

  4. Background: Distributed Source Coding Source Coding with side-information (Slepian–Wolf, Wyner-Ziv) ^ • X and Y are correlated sources • Y is available only at decoder X X Encoder Decoder Y Exploit side-information Y at the decoder while encoding X No MSE performance loss over case when Y is available at both encoder and decoder when innovations is Gaussian For the video coding case, X is the block to be coded and the side-information Y consists of the previously decoded blocks in the frame memory

  5. Y1’ YM’ . . . … Motion Vector … X X … Quantized … DFD Y1 Y1 YM YM . . . . . . Y1’ YM’ . . . Predictive Decoder PRISM Decoder Predictive Encoder PRISM Encoder ? X X Motion-Free Encoding? • The encoder does not have access to Y1’, Y2’, etc • Neither the encoder nor the decoder knows the correct side-information • Can decoding work? • Yes! • A “modified” Wyner-Ziv paradigm is needed (Ishwar, Prabhakaran, & Ramchandran ICIP ’03.)

  6. Y1’ Decoding failure Wyner-Ziv Decoder . . . YT’ X Wyner-Ziv Decoder bin index YM’ . . . Decoding failure Wyner-Ziv Encoder Wyner-Ziv Decoder X PRISM Need concept of “motion compensation at decoder”! Need mechanism to detect decoding failure In theory: joint typicality (statistical consistency) In practice: use CRC Robustness Comparisons: • Predictive Coding: channel errors lead to prediction mismatch and drift • PRISM: drift stopped if syndrome code is “strong enough”:Targeted noise ≥ Correlation Noise + Induced Channel Noise + Quant. Noise

  7. Auxiliary-Channel Coset Index Auxiliary-Channel Encoder Auxiliary-Channel Decoder Final reconstruction Wireless Channel X MPEG/H.26X Decoder MPEG/H.26x Encoder Xmain Wireless Channel MPEG/H.26x bit-stream ^ X Standards-Compliant Auxiliary-Channel • Secondary description of video sent over auxiliary-channel. • Need to find statistics of correlation noiseZ = X – Xmain. • Can leverage algorithm of Zhang, Regunathan and Rose (Asilomar ’99) to develop recursive correlation estimation algorithm. (Wang, Majumdar, Ramchandran, and Garudadri: PCS ’04.) • Auxiliary channel allows drift correction without intra-refresh.

  8. Results • Channel simulator provided by Qualcomm Inc. conforming to a CDMA 2000 1x standard. • Performance comparison among 3 systems: • H.263+ bitstream with 20% extra rate for FEC (RS codes) • H.263+ bitstream with 20% extra rate for standard-compliant auxiliary channel • PRISM • Standard-compliant auxiliary channel version outperforms H.263+FEC by 2.5-4 dB between error rates of 2-10%. • PRISM outperforms H.263+FEC by 6-8 dB between error rates of 2-10%. H.263+ with FEC H.263+ with Auxiliary Channel PRISM Stefan, 352x240, 15fps, 2200 kbps, 8% error rate

  9. PRISM for Wireless Video Broadcast Yb (“bad” side-information) Decoder Bad Xb Rate = R Encoder X • Broadcast source coding studied in information theory literature. (Heegard & Berger, IT’85, Steinberg & Merhav IT’04) • Lossy channel: need broadcast source-channel coding view. • Can use PRISM constructions. (Majumdar & Ramchandran, ICIP ’04) • No need to deterministically track Yb and Yg at encoder. • No need for multiple prediction loops  complexity savings. • Multiple side-informations at each decoder  motion search at each decoder. • Standards-compliant implementations possibly using the auxiliary channel setup. (Wang, Majumdar, & Ramchandran, ICASSP ’05) Decoder Good Xg Rate = ∆R Yg (“good” side-information)

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